Monday, December 29, 2008

Big Rain Event West Snow East

Issued Monday 12-29 11 amA strong weather system will move into the region later on Thursday, New Year's Day to bring some heavy rain to the lowlands of Western Washington. The forecast models have been consistent with this feature so I have a high level of confidence with this. Here are some early tentative rain amounts for the period Thursday New Year's Day 9 am to Friday 1-2-09 9:00 am for many location in Western Washington. Rain totals will be in the 0.75 to 1.25 inch range for this period. Some spots on New Years Day might start out with some light snow early but that will be short lived. For Eastern Washington the forecast is much more difficult since cold air will be in place so snow is certainly a good possibility. The amounts of water equivalent from Thursday New Year's Day from 10 pm to Friday 1-2-09 10 pm is from 0.40 to 0.80 in water equivalent. If that is snow and not rain that would be about 3 to 8 inches of snow.

Finally, the map below is for the forecast period Thursday New Year's Day at 4 pm. This map is 850 mb which is for winds at the 5000 foot level. Notice off the coast the winds are from the southwest at 50 to 80 knots. These winds will tend to draw moisture from the ocean and these strong winds and moisture will shift inland during the evening of New Year's Day and on Friday 1-2-09. Thus, strong winds and heavy precipitation will be the rule. After this front passes snow levels will drop close to the surface for Western Washington on Friday evening 1-2-09 and into Saturday 1-3-09